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#1
08-21-2022, 05:22 PM
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496452 Crank
According to online sites this is a 350 crank however I'm in the process of tearing down a second 400 which has this crank, first was a '77 557 block this 2nd is a 75 988 block, Both are standard bore however the rods are numbered on this 2nd one so I know someone has been into it at some point, don't see any evidence of anything weight being added to the crank for a re-balance.
Do late 350s and 400s pistons and rods weigh the same? I'm figuring it's late 70s, Friday afternoon 3pm and the factory line worker just grabbed the first crank he saw and sent it on down the line.
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78 T/A 4SPEED, Original paint, match #’s, mine since ‘99. 77 t/a sold 85 Monte Carlo SS sold 83 Mustang GT sold |
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#2
08-21-2022, 05:30 PM
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I do not know the exact weight difference between both pistons, but a guess would be that they are close enough that with how the factory puts the final balance on the whole assembled short block that things where close enough to be within tolerance.
Once again this is just a guess! One thing that I can say with confidence is that the 496___ part code is for 1975 only. PS. Now that I think about there was a year of 400 production where the top OD of the pistons had a pretty big chamfer added to them, and maybe this brought the weight of the 350 and 400 pistons very close. PS. Also if you have ever seen the Pontiac film taken in one of the engine assembly plants, a worker can’t just grab any crank and lower it in the block that may be in front of them! It’s a very informative film that I wish I could find again!
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I do stuff for reasons. Last edited by 25stevem; 08-21-2022 at 05:46 PM. |
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#3
08-30-2022, 11:30 PM
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I just opened up a early 1975 988 400 block. All stock and it has the same number crankshaft. I think it is funny how all the information on that number crankshaft it states they have narrow counter weighs. Just I also have a 4813 crankshaft and the counter weights are exactly the same thickness.
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#4
08-31-2022, 07:04 AM
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From what I have seen the narrow counter weights showed up with the chamfered top OD pistons.
Those chamfered top pistons where one of the worst things that Pontiac ever did! I can’t believe they where able to meet emissions standards with those ! Fuel that gets down there on the side of the bore that’s the furthest away from the plug either does not get used, or burns to late to add to power production, or may also lead to late fire detonation, Non of this is good!
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I do stuff for reasons. |
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